1. Field of the Invention
The invention relates to a process and an apparatus for printing and decorating various articles by means of inks of the type applicable by sublimation.
2. The Prior Art
As is known, many articles, even of common use, are at present printed or decorated by processes utilising special inks that can be transferred and applied by sublimation.
Sublimation is a direct transformation from the solid to the vapour state and the special sublimable inks, prepared on supports or sheets from fabric, paper or the like, transfer by sublimation from the sheets to the articles to be printed or decorated when said supports or sheets are kept closely adhering to the articles and heated.
Sublimation printing or decoration has many advantages compared to other decoration means.
In fact, ink vapours penetrate the printed material and generate vivid and very agreeable, resistant, no-thickness decorations, i.e. such as to support even a heavy wear or abrasion, with a high resistance also to the aggression of many acids and bases.
The best results are achieved with some plastic materials for the penetration in the same of sublimable inks, but all materials may be sublimation-printed if a an adherent paint layer is previously applied on the same.
Sublimation printing of substantially flat articles is easily realisable and is generally carried out with hot presses, which press sublimable-ink-bearing sheets on the articles to be decorated.
The temperature to be reached is comprised between about 180 and 215xc2x0 C., depending on the inks and colours utilised, and the pressure must suffice to ensure a direct touch between the plates and the articles. Sublimation printing of articles of various shape and size is much more complex.
In this case, special apparatuses are generally employed that are provided with silicone elastic membranes, very soft and thin, between which the articles to be printed are inserted.
The supports or sheets carrying the sublimable ink are interposed between the articles and the membranes. Suction pumps create vacuum between the membranes, so that they adhere to the articles, stretching and pressing the inked sheets. Then heat is applied to reach said ink-sublimation temperatures.
This known technique has many drawbacks. There has bee realised a process for the production of large-size, variously decorated sections, which was the subject matter of the International Patent application PCT/EP96/00656, filed on Feb. 2, 1996; the process comprises the steps of winding of the artefact, previously subject to a surface treatment of pre-painting, anodic oxidation and the like, in a transfer support carrying the wished decoration; covering the section wrapped in the support with a membrane from rubber or the like; vacuum formation by means of suitable ducts between the membrane and the section wrapped in the support, an prior interposition of means suitable to ensure air flow and outlet, so as to cause the support to closely adhere to the shape of the artefact, and complying means suitable to obtain the uniformity of the pressure exercised by the membrane; and lastly heating the whole so as to obtain the transfer of the pattern and the polymerisation of colours.
A first drawback is due to the very fact that the approaching of two membranes to the articles determines connection zones between the membranes in whose correspondence adhesion is lower. There exist therefore zone wherein printing does not take place or takes place with a quality lower with respect to other zones. Besides, if the surfaces to be decorated are very irregular, the membranes poorly adhere in any case to these surfaces.
It is not possible to obviate this drawback by increasing the pressure exercised on the membranes, which remains limited to the atmospheric pressure, to cause the same to adhere to all points of said surfaces.
Neither is it possible to vary pressure according to sites, for instance to nuance the impressed decoration. The number of articles that can be printed each time is also reduced and depend on the size and the weight of said articles. The weight is important as it is supported by the membranes.
On each working cycle, the membranes are submitted to a marked stretching: said membranes deform many time each day to adjust to the wrapped articles, and in these conditions they undergo a high temperature heating.
Therefore, they loose their elasticity in a short time and adhere with an increasingly lower precision to the most irregular shapes. This drawback is important as the membranes in question are very expensive and cannot be immediately replaced if only a partial loss of elasticity has taken place.
Moreover, the articles to be decorated must be free from holes or sharp edges, to prevent membranes from slitting or breaking.
Therefore, it is indispensable to carry out a starting work of preparation of the articles to be printed, with a provisional closing of holes.
The preparation work must be carried out also for the interposition of the supports or sheets bearing the sublimable ink: actually, the same require great preparation ability, as the blind membranes cover the support, preventing a clear perception of their positioning.
Neither is it possible to keep for a long time the articles between the membranes, once ink sublimation has taken place, as the apparatuses must be used uninterruptedly, to reduce the incidence of the cost of the same on decoration operations.
As a consequence of the above, when the printed articles are collected, the still hot ink solvents give off in the environment, affecting the operators adversely and polluting the atmosphere.
Lastly, it must be stressed that the colours that have undergone the sublimation chemical process deposit partly on the membranes and that these colours may partly pollute the subsequent printing operations.
Thus, it is also necessary to provide for a continuous cleaning of the membranes, with an increase in global costs.
In this situation, it is an object of the present invention to provide a process and a sublimation printing apparatus able to substantially obviate the aforesaid drawbacks. Object of this invention is also to provide a process allowing to obtain large size sections having a length of up to 20 m, variously decorated, to be used for the production of doors and windows, also for outdoor use, having the requirements of quality, weatherproofing and resistance to ageing, provided for by the different international norms and by quality marks.
A further object of this invention is to provide a process for the realisation of sections, in particular from metal, aluminium and aluminium alloys, plastic materials, composite materials (such as resins reinforced with carbon and or glass fibres and the like) provided with decorations in one or more colours, such as geometric, floral, imitation wood, imitation marble decorations, and also decorations comprising very complex patterns, exempt from defects such as deformations of pattern edges, smears, diffusion and superposition of colours and the like, and using a process with a low manpower need.
Still a further object of the invention is to provide an apparatus suitable for realising said process for the decoration of said sections.
The specified technical task is substantially achieved by a process and an apparatus for printing and decorating by means of sublimable inks characterised in that they comprise any of the new technical solutions described hereunder and claimed, or any combination of the same.